Gold Nanopyramids Assembled into High-Order Stacks Exhibit Increased SERS Response

• Published in: The journal of physical chemistry letters 2010-04, Vol.1 (7), p.1046-1050
• Main Authors: Stoerzinger, Kelsey A, Hasan, Warefta, Lin, Julia Y, Robles, Alex, Odom, Teri W
• Format: Article
• Language: English
• ISSN: 1948-7185
• DOI: 10.1021/jz100095b

This Letter describes how gold pyramidal nanoshells (nanopyramids) can be assembled into low- and high-order structures by varying the rate of solvent evaporation and surface wettability. Single-particle and individual-cluster dark field scattering spectra on isolated, dimers and trimers of nanopyramids were compared. We found that the short wavelength resonances blue-shifted as the particles assembled; the magnitude of this shift was greater for high-order structures. To test which assembled architecture supported a larger Raman-active volume, we compared their surface enhanced Raman scattering (SERS) response of the resonant Raman molecule methylene blue (λ(ex) = 633 nm). We discovered that high-order structures exhibited more Raman scattering compared to low-order assemblies. Finite-difference time-domain modeling of nanopyramid assemblies revealed that the highest electromagnetic field intensities were localized between adjacent particle faces, a result that was consistent with the SERS observations. Thus, the local spatial arrangement of the same number of nanoparticles in assembled clusters is an important design parameter for optimizing nanoparticle-based SERS sensors.